|Snow Peak, Mount Monadnock, Marlborough, NH|
This week I wanted to share a simple technique to obtain multiple (or at least two) images for focus stacking while hand-holding the camera.
I have previously discuss in considerable detail the technique of focus stacking to achieve deep depth of field. This approach
requires multiple images focused at different planes of the scene which are then combined in post processing to achieve sharpness throughout. A key requirement of the technique is that the images all be framed to match when aligned in the computer. With sophisticated software, such as Photoshop, the match does not have to be perfect, but typically this is best achieved with the camera locked down on a tripod. It can be quite challenging to manually vary focus while trying to hand-hold the framing perfectly constant. This is where my camera's auto focus points can come to the rescue.
I have never been a big fan of auto-focus for my landscape
|Hibernation, Pomfret, Vt. Two focus planes.|
Most photographers are familiar with the technique of holding the shutter down half-way to lock focus on a part of the scene and then recomposing for the final shot. This is most frequently used when focusing a subject that is off center, but the same technique can be used to grab a couple of images for a simple focus stack. In the example of Mount Monadnock shot from Marlborough, New Hampshire, I locked focus on the detail of the fence and then re framed to include the distant mountain. The first image caught the fence in clear focus and then without moving the camera I locked focus on mighty Monadnock and shot again. As I shot the first image I carefully noted the position of the central focus point square to assist in close alignment of the second image. In more complicated situations, fully sharp focus stacking can require more than two images, but in bright light, when I can stop down, two are often enough to get good results, especially when there are just two discrete planes of interest.
|Canon 5D Mark II Focus points|
Mill Ice, Harrisville, New Hampshire
My Canon 5D Mark II has 9 focus points displayed on the screen, but only the central square is a cross sensor, vertical and horizontal, and therefore the most accurate. When possible I try to use the central point for focus stacking but there are many times when the central point aligns with neither the foreground or background in my desired composition. Faced with this situation I can usually find one of the other focus points that will provide the coverage I need. In my image of the frozen mill pond in Harrisville, New Hampshire, I angled the camera down to using the top focus point to lock in the sharpness of the foreground ice and then recomposed. In my second image, the focus point was in perfect position to catch the iconic Harrisville Public Library.
Using one of the 8 peripheral focus points can reduce the reliability of the auto-focus, especially in dim light or low contrast. To help, I have switched my focus lock from the shutter to a button on the back of the camera that doesn't require continuous pressure to maintain the focus. In the mill pond image, I could lock the foreground focus with the central point and then switch to the upper point ready for when I refocused on the background. Not all cameras can switch the focus button. The directions for mine were buried in an obscure corner of my manual, but, with practice, the ability to lock focus without having to hold the shutter down, works well for me in most situations.
|Focus Button on Back of the Camera|
|Ashuelot River, Keene, NH, |
Multiple Focus Planes
The trick with this technique is to hold the camera steady as you re-press the shutter and to learn how to move the focus point around the screen. I have gotten good enough that I will occasionally try to move the focus point within the screen to catch more than just two images for stacking. The more manipulations I try, the harder it is to maintain the frame, but Photoshop can do some amazing things with auto-alignment. Still it is about at this time that I grab for the tripod.
The speed and accuracy of auto-focus in modern cameras is amazing and improving all the time. I still like to use manual focus in many landscape situation but it is important to understand your camera's focusing capabilities and to use them when the time is right.